Mining and recovery of potash compounds



1943. I R cnoSs; 2,331,890

MINING AND RECOVERY OF zogmsa COMPOUNDS 1 Filed July 5, .1941 :5sheets-sheet- 1 V fly /056 Patented Oct. 19, 1943 MINING AND RECOVERY OFPOTASH COMPOUNDS Roy Cross, Kansas City, Mo., assignor to Kansas CityTesting Laboratory, Kansas City, -Mo., a

corporation of Missouri Application July 5, 19 41, Serial No. 401,104

8 Claims.

This invention relates to an improved process of recovering potassiumsalts from brines and ores containing them, and the present applicationis in part a continuation of my co-pending application Serial No.267,506, filed April 12, 1939, which in turn is a continuation of myapplication Serial No. 136,178, filed April 10, 1937, now matured intoUnited States Patent No. 2,161,800.

In the present methods of mining and recovering potash, ores are minedby shaft, room and pillar type of mining, analogous to ordinary shafttype coal mining. It is necessary to leave large amounts of the oreunderground for pillars, walls, and ceilings, in order to assure safeworking conditions and support. In the Carlsbad area in New Mexico,sylvinite is mined in this manner but only-50% to 60% of the ore isremoved from the deposits. As shown in my earlier application which usesasuperheated liquor for dissolving potash salts from deposits,substantially all of the potash salts are removed from the deposits,leaving most of the sodium chloride in situ. In the course of thisremoval of potassium salts, a certain amount of sodium chloride isalways present in the circulating liquor, One of the objects of thepresent invention is to provide a novel means of recovering thepotassium chloride from the hot brine without recovery of this sodiumchloride. Obviously, this is of advantage over the present method'ofelevating the ore mixture of potassium and sodium chloride to thesurface, separating the potassium chloride and sodium chloride, anddisposing of the sodium chloride. This disposal of sodium chloride is asource of considerable trouble at -the present time, it being allegedthat streams are polluted thereby.

In the present art, the recovery of potassium chloride from sylviniteore is done in two ways, one of which comprise a flotation andclassification system dependent on selective wetability and on thediflerence in specific gravity between potassium chloride and sodiumchloride, while the other depends upon a leaching of the sylvinite orewith warm water at atmospheric pressure. The amount of equipment toproduce 1,000 tons of potassium chloride per day by ordinary leaching istremendous, since the brines must be recycled slowly in great quantitiesto. dissolve the salts at this rate. Another object of the presentinvention is to provide a more emcient and economical method forproducing potash from sylvinite.

Other objects and advantages of the invention will be apparent byreference to the following description in conjunction with theaccompanying drawings, in which:

Figure 1 is a diagrammatic or schematic illustration of amining andextracting operation performed in accordance with the present invention;

Figure 2 is a chart showing the solubility of various materials that mayadvantageously take part in the practice of the invention as applied tosylvinlte;

Figure 3 is a diagrammatic or schematic illustration of anotherembodiment of the invention;

Figure 4 is a cross-sectional view taken along the line 4-4 of Figure 3;t

Figure 5 is a cross-sectional View taken along the line 5-5 of Figure 3.

Figure 6 is an elevational view with parts broken away of a modifiedform of the invention illustrating a reflux vaporization vessel 40 ofthe type shown in Figure 1 in series with a precipitation tank I58 ofthe type shown in Figure 3.

For purposes of description, a typical operation on sylvinite as thesalt ore will be relied upon. Curves 3 and 4 in Figure 2 show theconcentrations in pounds of potassium chloride and sodium chloriderespectively, per pounds of water. The respective illustrative maximumand minimum temperatures contemplated in this description, and thesolubilities of the salt thereat are as follows:

It should be borne in mind that any increased concentration of the brinesolution will precipitate sodium chloride. I

In a mining operation, high pressure is of advantage in securingpenetration into the bed as an aid to the high temperature of thesolution for dissolving potash salt, although this is-not so importantin the extraction above ground from ores that have been broken up.

Referring to Figure 1, the operation in accordance with this inventionas described now is the mining modification. Assuming the process to bein operation, one cycle will be described for recovering potassiumchloride from an underground deposit of sylvinite. A mother liquor, thecomposition of which is substantially a solution as follows: A well hasbeen drilled into the potash bed, the bottom being approximately levelwith the bottom of the deposit. A large casing 16 is set in the well,the bottom of the casing being set approximately level with the top ofthe deposit. It is desirable to tightly seal the casing to thesurrounding formation to prevent pressure leaks and also to insulate thecasing.

A surface pipe is often desirable. Inside of casing 16 is set smallerdiameter production pipe 18. The bottom of pipe 18 is near the bottom ofthe potash bed and its top passes through pipe l6 above ground in apressure tight joint. The

superheated unsaturated brine passes downwardly in the annular spacebetween pipes l6 and I8 and into the potash deposit where it dissolvespotassium chloride. It should be assumed that a pool of liquor in thedeposit is being substantially saturated with potassium chloride andthat the hot brine is added to the pool. The hot brine is introduced tothe bottom of the pool and gives a stirring action as it travelslaterally across the pool. The equilibrium in the pool is disturbed andmore potash is dissolved from the faces of the potash bed.

It is characteristic of potassium chloride that it takes up heat uponbeing dissolved, and therefore the brine becomes cooler and, during itsdissolving action travels downwardly along the face of the potash wall.Some radiation of heat takes place into the salt deposit and into theearth above and below the deposit. Also heat equal v to the specificheat of both the potassium chloride being dissolved and the sodiumchloride remaining, must be furnished. As the brine becomes saturated,it again travels horizontally at the lower part of the pool toward thewell where it is released upwardly through production pipe l8. The brinehas lost some of its original heat in radiation and in heat of solutionof potassium chloride, and therefore is cooler as it travels upwardly inpipe l8, than is the downgoing liquor surrounding the pipe. This is animportant arrangement because the upcoming brine is saturated withrespect to potassium chloride and any cooling effect would precipitatepotassium chloride and clog the production pipe. From production pipe[8, the superheated saturated brine passes through valve 80, conduit 86,and pressure release valve 38 into separator 40, Conduit 66 is wellinsulated or heated to prevent drop in 20a. It should be noted thatconveyor housing 48 preferably extends above the level of the pool ofbrine in separator so that a draining action may be obtained.

When the vapor has flashed from the brine, it immediately comes incontact with vapor precooling coils 32 and thence passes to condenser26. The vapor is thus completely condensed and the condensate, beingpure water, refluxes downwardly into the pool of the separator. Thiswater condensate continually washes the condenser and coils and keepsthem clear of, salts. In some instances, it is desirable to have anauxiliary condenser to insure complete refluxing of the vapors. Thiscondenser may be cooled in any suitable manner.

The rate of flow of the liquor through separator 4D is slow enough thatthe desired minimum temperature can be reached. The cooled brine passesout of separator "through conduit which is arranged to form a sealagainst the escape of vapors from the separator. The brine empties intotank 20.

The potassium chloride salt in zone 42 has 'come down substantially freefrom sodium chloride, due to the fact that the solubility of the sodiumchloride is approximately the same at the temperature of the brine. Thebrine passes into the body of liquid in separator ill and part of itimmediately flashes into vapor, thereby cooling the brine andprecipitating potassium chloride. Baiiles ll prevent the mechanicalelevation oi. salt into condensing coils 32 and condenser 26. The hotbrine may be introduced either above or below the level 01 the liquid inseparator 40. The bottom of separator ll is conical or hopper shaped toform a precipitated potash collecting zone12. In the bottom of zone 42is a conveyor arranged to pick up the precipitated potash and carry itto stock pile low temperature of the pool as it was at the hightemperature in the deposit. The material in the stock pile will containsome moisture which is in the'form of the saturated potassiumchloridesodium chloride cold brine. The salt may be washed with asolution saturated with respect to potassium chloride, thus removing allsodium chloride. It is then dried and treated in a suitable manner forcommercial sale.

Since it is desirable to maintain the pool of liquor in the potashdeposit full of liquid, makeup fluid is added to tank 20 or at somesuitable point. The make-up fluid is added in a volume equivalent to thevolume of salts removed from the deposit. Brine seepage is also made up.The make-up fluid is ordinarily plain water. If

- it is convenient to make a sodium chloride brine for make-up fluid,this may be done in order that.

there will be no solution of sodium chloride from the deposit.

The cool brine is circulated from tank 20 by pump 24 through line 22into condenser 26.

The rate of circulation of the brine through condenser 2a issufllciently fast to prevent the brine from absorbing more than enoughheat to raise it to approximately its boiling point. Thus, the coolestbrine is the cooling medium for the condenser in what ordinarily is thefinal refluxing stage of the condenser. An important feature of theinvention is the fact that in many instances approximately the amount orbrine in the system can be used as the cooling medium for condensing thevapors and absorb a considerable quantity of heat from the vapors priorto being reheated in'the heater 34. This makes for economy of operationand equipment. From condenser 25 the brine passes through conduit II andis pumped by pump III at high pressure through vapor precooling coil 32of the separator and thence is recycled through the system heretofore.described The circulating of the brine at high pressure through coil 32is an important feature of the invention inasmuch as it allowssufllcient precooling of the vapors by a brine which is already underpressure and therefore need not vaporize to allow a complete flnalabsorption ofhea-t from the vapors by condenser 28 where the coolingmedium is at or near this extraction,

been dumped into salt basin 88.

assnseo T atmospheric pressure. If precool'ing coil 82 is not used,condenser 26 must be'larger in order to accomplish its purpose and alarge amount of cooling agent other than the recycling brine isrefluxed. The factors controlling this feature are the final temperatureof the brine introduced into the potash bed and the amount of make-upwater required to replace the volume of salt taken from the bed.

It is'sometimes of advantage to pass the makeup fluid through auxiliarycondenser i? before adding it to the brine to be recirculated.-

A modified application of the invention is an operation Where the saltis dissolved from an ore which has been brought above ground and placedin extractors. For purposes of description it is assumed that the ore issylvinite and that the salt desired to be recovered is potassiumchloride. Multiple extractors are used so that while the ore in two ofthe extractors is being contacted with brine, the third extractor may befilled with chloride, extractor 54 is cut out o! the system and thesuperheated brine enters extractorbt through valve its, exits throughvalves cc and "12, conduit we and valve ltd, into extractor 52, valve 92ore, thus making a continuous system. Any I number of batteries ofextractors may be used. Since the treatment of the brine in variousstages has been described in connection with the mining operation, thisdescription will describe a typical cycle in the recovery of thepotassium chloride from sylvinite ore.

Well it is by-passed from the system by closing valves 88 and 8%. Motherliquor is superheated in heater and passes through valve it, conduit 58,and valve l2, into extractor $2. The rate of flow is such that the brineissuing from the extractor is substantially saturated with potassiumchloride. The saturated brine circulates from extractor 52 throughconduit 6t, valve 76, conduit it, valve it, conduit to, and pressurerelease valve 38, into separator cc. Potassium chloride crystallizes,settles and is carried out by conveyor '45 to stock pile 28a. The brineis cooled by reflux vaporization without concentration of the brine andthe potassium chloride recovered as described in' the mining operation.The cooled brine leaves separator an .by conduit 50, falling into tank29. It is then recirculated by pump 24 through conduit 22, throughcondenser 2t, conduit 28, high pressure pump 36, and vapor precoolingcoils 32, to-heater as previously described. In this instance, it is notnecessary to add any considerable amount of make-up fluid since there isno requirement to fill a cavity as in the case of the mining operation;

When most of the potassium chloride has been extracted from extractor52, valve 13 is closed and the brine passes through valve 82 intoextractor 54, and thence to the separator it through conduit 62, valves5% and 86, conduit 66, and pressure release valve 38,, and the cycle iscontinued. In this manner unsaturated brine cleans up the ore residue inextractor 52 before entering extractor 55. When the ore in extractor 54is nearly exhausted of potassium chloride, extractor 52 is by-passed andthe superheated brine enters extractor 54 through valve 88 and exitsthrough conduit 62 and valves 85 and 98 into extractor 56, valve 86being closed. In this manner, the unsaturated brine passes through themostly exhausted ore in extractor 5d, thence through extractor 56 beingclosed. From extractor 52, it continues through conduit to, valve N,valve i8, conduit 86, and pressure release valve 38, into separator 4c,and the cycle is continued. In the meantime, the sodium chloride andother residue %is dumped from extractor ed and the extractor isrecharged with fresh sylvinite. In this manner, the most completeextraction of the ore maybe obtained at a given rate of flow of thebrineby thus continuously rotating the flow through the extractors andcontinuous operation is maintained.

Only one extractor may be used,or only two extractors may be used, thelatter being the more desirable.

The novel method'of o ling a saturated brine .to obtain crystallizationof a desired salt is a great improvement over the presentart,particularly when it is combined with the feature of preheating thecooled brine by passing it in heat exchange relationship with the vaporsto be condensed and passing the brineagain through the heater. Equipmentrequirements are much smaller than in the present art. Highercirculation rates may be continually used and mechanical coolingdifiiculties are eliminated.

On properties already in operation by shaft mining methods, it isdesirable to decrease the production costs of at least part of the oremined by using the well type method covered in my co-pendingapplication, and to also continue the use of the shaft mining equipment.Thus, it is convenient by using one system to extract salt fromunderground and from ores brought above ground, in a combination unit asshown in the drawings. J p

This invention has another feature which is important. This featureconsists of adding to the saturated brine entering the separator or inthe separator, a volatile vaporization agent having a boiling pointlower than that of the brine. In this modification of the'process thevolatile liquid, in which potash not more than slightly soluble, iscontinuously added to the brine, continuously vaporized from the brineto eliminate the vaporization of water from the brine, condensed bysuitable means, and continuously recycled into the brine for furthercooling by vaporization. An arrangement of an outside condenserconnected to the separator and means for recycling the vaporizationagent is shown in Fig. 3. The cooled brine may be circulated through thecondenser in heat exchange relationship with the vapors in the samemanner as with the previously described system.

I sometimes cool the brine in two stages, the

I Figure 1 is shown in series with the precipitation and out throughconduits E i and 96, valve 92,

fresh ore, the sodium tank wt of Figure 3. The conduit 50 is connected.directly to the conduit I48 and all other numerals indicate like partsof the apparatus as previbusly described.

It is preferred that the volatile vaporization agent be one which isimmiscible in the brine, although this is not a requirement.

A miscible vaporization agent may alsobe easily separated from the brineleaving the separator 40 by distilling oil any traces of the agent by aseparate still treating the brine or by passing the brine in heatreceiving relationship with the hot unsaturated brine leaving thecondenser coils 26 or 02. Petroleum ether, butane or pentane may beused. Examples of other vaporization agents are suliuric into conduitI48 through valve I60, which is normally open, to a distributing memberI52, which distributes the hot liquid having a relatively high ether,benzene, alcohol, low boiling point gasoline hydrocarbons, acetone, etc.

In Figure 1, pre-coolirm coil 82 has been illustrated diagrammaticallyas being in heat exchange relationship with the vaporizing zone 01'separator 40 which in turn is in direct communication with refluxcondenser coils 26. Since the vapors are preferably brought into contactwhile still under pressure with pre-cooling coil 32, it will readily berecognized that coil 82 may be in a separate pressure chamber into whichthe vapors. are first flashed and then released to the reflux condenser26. Any other suitable modification or arrangement of the apparatusillustrated may be used to accomplish the same purpose, namely,contacting the flashed vapors while still under super-atmosphericpressure with the pre-cooling coil in which the circulating liquid islikewise under superatmospheric pressure. In this manner, thebrine isdepressured in several stages. An important feature of the system isthat the hot brine containing salts is not brought in contact withcooling coils which would make a hard precipitate of the walls of thecoils.

In carrying. out the process described it is highly important to preventpecipitation of salts due to cooling in production pipes I8 and 66; Asalready indicated, this may be accomplished by heating the conduits toslightly unsaturate the solution contained therein. An alternativemethod is to maintain the rate of circulation of the dissolving materialinto and out of the potash deposit sufliciently fast to dissolve lesspotash than will form asaturated solution at the temperature of theproduction pipes above ground.

It is sometimes desirable to filter the potash brine before passing itinto the separator in order to remove impurities such as dirt, ironcompounds, etc., although usually settlement takes place in the deposit.

One of the preferred embodiments of this in-. vention is illustrated inFigures 3, 4 and 5. As shown in Figure 3, in this embodiment a brine issuperheated in a heater IIO, then pumped through a conduit II2controlled by a valve II4 by means of a, pump II6 thence through aconduit II 8, controlled by valves I20, I22 and I 24 into a conduit I26.The conduit I26 passes through a casing I28 into a potash bed I30 andthe superheated brine from the conduit I26 impinges against the far endI32 of the potash bed, causing a backward horizontal component ofcirrculation along conduit I26 into the space between conduit I26 andcasing I28. The liquid passing backward is substantially more saturatedwith respect to potash than the entering liquid. This more saturatedliquid passes through an exit in the casing I28 into a conduit I34,thence through a conduit I36 to pump I38; Valve I24 and pump I38 coactto keep pressure of the liquid in the potash bed to a desired maximum,when desirable. Valve I24 is closed to the degree necessary to decreasehydrostatic head on the bed and pump I 38 iorces the saturated brineupwardly. In normal operation the valve I40 controlling conduit I36 isopen and valve I is closed. The liquid in conduit I36 is pumped by meansof pump potash content in a body of liquid I 64 below the liquid levelI66. The body of liquid I64 is contained in what is termed a primaryprecipitation tank I68. The size of this tank may vary depending uponthe volume of liquid being processed and other factors.

In the central part of the tank I68 is an open ended pipe or well I60with one end disposed in the body of the liquid and the other end abovethe liquid level. Also disposed in the body of the liquid is a bubblerconduit I62 provided with a number of fine holes, spray-nozzles, onsimi-- lar devices I64 through which a volatile vaporizable liquid ispassed and vaporized simultaneously or contemporaneously. This volatileliquid,

and the potash therein, being less soluble in the cold than the hotliquid, is precipitated and carried by means of a, conveyor I66 or othersimilar device, in an upward direction in the manner shown so that as itmoves upwardly in the conveyor, the entrained liquid tends to flowbackward down the conveyor shaft I68. The remaining solid iscontinuously dropped onto ,a pile I10, or into any suitable containeroutside of the primary precipitation tank.

A conduit I12 passes through the wall of the tubular casing I 60 andresidual liquor is withdrawn from the primary precipitation tank I58through this conduit. The residual liquor passing through conduit "2enters conduit I18 through valve 212 controlled bythe liquid levelcontrol device 268 by means of arms 210 and then passes to conduit I80,from which it enters a secondary precipitation tank I82 at a point belowthe liquid level I84, as illustrated in Figure 3. Valve I16 in conduit I14 is normally closed but in certain instances it may be desirable tobypass valve 212 by opening valve. I16. In the secondary. precipitationtank I82, further precipitation of salts occurs due to the influence 0fthe cooling coils I86. Precipitated salts are carried from the bottom ofthe precipitation tank by means of a conveyor mechanism dropped onto apile I80 in the manner illustrated. Residual mother liquor is drawn offby means of a. conduit I92 and is pumped by means of a pump I84 througha conduit I98 into a condenser I88 where it assists in cooling andcondensing the butane, or other volatilized liquid previously employedas a direct cooling medium in the primary precipitation tank I58. Themother liquor passing through the condenser I88 enters a, conduit 200through which it passes to a conduit 202 controlled by valve 204.Generally it is desired to return thismother liquor to the It will beunderstood thatmany diiierent types oi heaters may employed and hence,the parl88 and ticular structure of the heater will not be described indetail. In some instance it may be desirable to by-pass a part or all ofthe liquid passing through conduit 42 to a conduit MB. In this latterevent, the valve 206 is closed or partly closed and the valve 853 isopen or partly open, permitting the by-passed liquid to go as arefrigerant and simultaneously cooling the body of liquid i5 1 and thehot liquid entering through the distributing member H52. The volatilizedvapors or gases rise upwardly in primary precipitation tank I58 and themist is largely separated therefrom by a mist screen 2i ,6. The gasesand vapors which pass the mist screen 2 lb enter a conduit 2l8 fromwhich they pass into a suction chamber 220. From the suction chamber220, gases or mixtures of gases and liquids, are passed through aconduit 22d controlled by a valve 226 and are compressed by means ofcompressor'228, after which they are passed throughconduits 230 and 232into a pressure condenser 230 where they are converted substantiallycompletely to a liquid form. The volatilizable liquid passes fromcondenser 230 through a conduit 236 to a cylinder or reservoir 238 whereit is held under pressure suficient to maintain it in a liquid stateunder the existing temperature conditions. From the reservoir 238, theliquid is passed through conduits 240, 242, 240, 246 and valve 208 tothe distributing conduit 182. In this manner the volatile liquid iscontinuously re-cycled in the process and the refrigerating effectthereof is utilized over and over again.

Figure 4 is a cross-sectional view of the primary precipitation tanktaken along the line -4 of Figure 3, and Figure 5 is a cross-sectionalalong the line 5-5 of Figure 3.

In the foregoing description certain by-pass arrangements are notdescribed. These arrangements are intended to be used under certainspepump MB is by-passed by conduits 250, 252 and 25 3, controlled byvalve 256. It willbe understood that the valve 258 is normally closedunless the by-pass arrangement is being used, in which case valve H4would be closed. This bypass arrangementmay be employed where the pumpis unnecessary, as, for example, where a source of a salt containingliquid-is available under superatmospheric temperatures and pressures.Conversely, pump H6 may furnish pressure to circulate brine into and outof the potash bed to the surface where pump I38 is by-passed.

A second arrangement of conduits compris- 255, is provided to circulatesome hot unsaturated potash carrying liquid into conduit M2 to preventprecipitation on the way to the cooler I58. This is accomplished bypartly op ning valve 284, and. partly closing valve I24. Valve I22 isopen. This is an important feature of the invention. Since the onlymeans of heating the potash bed and pool therein is by heat transingconduits 258, 260 and 262 controlled by valve ferred' from the brinecirculated to the bed, the amount of heating in the bed is limited toheat available from the circulated brine. Furthermore, the amount ofbrine circulated to obtain a desired rate of potash production per unitof time is usually insumcient to furnish the desired amount of heat tothe bed and pool. To overcome this difficulty part of the brine from thedeposit isrouted through the cooler and another part is by-passed andrecycled through the heater without, cooling, and thu transfers view ofthe secondary precipitation tank taken cial circumstances or conditions.For instance,

more heat in the potash bed. Another means of accomplishing this featureis to onli Partially cool and precipitate a large quantity of brine inthe cooling stage of the operation, thus giving greater heat transfer inthe bed than would be available if only the brine necessary to provide'a given production rate of potash were used. This however requireshandling larger volumes of liquor in the cooling stage. ,A pressuregauge 200 is proved in order to indicate the pressure of the liquidflowing in conduit 502. The liquid level in the primary precipitationtank i583 is maintained substantially constant by a liquid.

level control device 208 provided with arms 2% controlling the openingand closing of valve 212 in conduit W8. A similar device 2% maintains.

a substantially constant liquid level in tank 238 in conjunction witharms 27% and valve 270.

A typical illustration of the operation of the foregoing process is asfollows: The solvent liquid passing through heater H0 is heated to atemperature of between 400 and 000 F. The pump H 3 pumps the at about 50gallons per minute under a maximum of about 500 lbs. per square inchpressure. The pump H38 pumps the solvent more saturated with respect-topotash atabout 50 gallons per minute'under a maximum of about 600 lbs.per square inch pressure. Pump 0% is suitable ior pumping the motherliquor at 50 gallons per minute under 500 lbs. per square inch pressure.The butane tank 238 is under a pressure of about 125 lbs. per squareinch and the condenser 200 is under approximately the same pressure. Thetemperature of the more saturate liquor entering the primaryprecipitation tank from conduit M0 isaround 300 to 500 F. Thetemperature of the liquor leaving the primary precipitation tank 558through conduit H2 is around 200", F. The temperature of the brineleaving the secondary precipitation tank 82 through conduit 892 isaround 60 to F.

As illustrated, a portion of the butane in conduit 240 is directedthrough conduit 200 controlled by valve 282 to cooling coils 180 fromwhence it passes through conduit 280 to suction chamber 220. Thereafter,it is re-compress'ed by compressor 220 and condensed in condenser N0, asalready described.

In practicing the invention it is possible to recover and mine thepotash from a plurality of separate beds. As is well known, manypotashdeposits lie in multiple beds of comparatively thin character, forexample, from 6 in. to 3 ft.

in thickness. By ordinary methods these beds cannot be mined practicallybecause working brine heated solvent liquid mented. At predeterminedpoints opposite the beds of potash pieces of a soft material are placedin the casing which are of such nature that they can easily be cut outand removed. These are usually of an aluminum type and one casingsuitable for this purpose is called by the trade name Securalloy. Whenthe casing has been properly set and cemented, a drill bit and reamerare used to cut out the soft aluminum casing and any cement back of itthus opening up the formation at the desired horizon and leaving thecasing tightly cemented otherwise. The liquid mining of the potash maythen be carried out in the manner herein described. The particularmethod of dissolving the potash from the vein may be, for example, anyone of the methods described in my U. 8. application Serial No. 278,663,filed June 12,1939, now Patent No. 2,251,916 issued August 12, 1941. Byboring a series of holes in the casing at the proper levels, a pluralityof potash deposits may be mined simultaneously. This is preferablyaccomplished by directing a jet of liquid laterally along the potashvein in the direction in which the potash is to be mined therebyprogressively creating a channel in the potash and causing a backwardcomponent of circulation toward an exit conduit along or within thecasing, or to another exit hole. Thus, where horizontal circulation isobtained, beds of 3 ft. thickness will average the value of a single bedin the pres ent operations having a 15 ft. thickness.

In some ores such as polyhalite, it is of great value to use asuperheated solutionof a salt for contacting the ore which, under heatand pressure, will convert the salt desired to a more soluble form.Thus, the use of sodium chloride or calcium chloride brine for themining of poly halite and obtaining potash and magnesium salts aschlorides rather than sulfates, is highly desirable.

The use of superheated brines or dissolving liquors for extractingreduces the production of calcium sulfate as an impurity and this is animportant feature of the invention. Also, the mother liquor being abrine contributes a better heat transfer in the heater than would plainwater.

In order to reduce corrosive action of the brine of the process, the pHof the brine may be raised by adding a convenient alkaline agent.Calcium or sodium hydroxide is usually satisfactory for this purpose.Inhibitors such as nicotine, arsenious oxide, quinoline ethiodide andthe like are added to decrease or eliminate corrosive effects.

becomes more concentrated with respect to potassium chloride, the stepsof passing said more concentrated liquor into a substantially constantvolume body of a relatively cooler mother liquor whereby potassiumchloride is precipitated, refluxing and returning to the body of pounds,passing said heated solvent liquor into a In attacking refractory ores,it is desirable to add CO2 gas to the water being charged into the ores.In such cases the C0: is recovered by release of pressure and sent backinto the well with the entering brine.

Where bromine and iodine occur with the potash ores, it is convenient totreat the brine at intervals with chlorine and steam to recover suchbromine and iodine by fractional condensation.

Having thus described the invention, what I claim as new and desire tosecure by Letters Patent of the United States is:

1. In a process of mining sylvinite from subterranean deposits thereofand of recovering potassium chloride therefrom wherein a heated solventliquor unsaturated with respect to potassium chloride is circulated incontact with saidsubterranean deposit of said ores, circulating saidsolvent liquor in contact with said subterranean deposit until saidliquor becomes more concentrated with respect to said potassiumcompounds, removing said solvent liquor from said subterranean depositand passing it into a main body of mother liquor, separating potassiumcompounds from said mother liquor, continuously removing a portion ofsaid mother liquor from said volume of liquor and subjecting it tofurther cooling, separating a further amount of potassium compounds fromsaid further cooled .portion of said mother liquor, adding to said mainbody of mother liquor a water immiscible volatilizable liquidvaporizable at the temperature of said mother liquor, continuouslyvolatilizing and condensing said solvent and using a portion of saidsolvent for the further cooling of the portionof mother liquor withdrawnfrom the main body thereof.

relatively more concentrated liquor out of the sylvinite deposit,circulating part of said liquor to a depressuring and cooling zone andrecirculating the other part of said potash liquor through a heatingstage and thence through the sylvinite deposit.

4. A cyclic process of mining potassium compounds from undergrounddeposits thereof which comprises establishing a zone containing a mainbody of an aqueous mother liquor which is a solvent for said potassiumcompounds when unsaturated with respect thereto, withdrawing from saidmain body of mother liquor a portion thereof, heating said withdrawnportion of mother liquor whereby to produce a solvent liquor unsaturatedwith respect to the potassium compounds to be mined, passing said heatedsolvent liquor into a subterranean deposit ofsaid potassium compounds,circulating said solvent liquor in contact with said subterraneandeposit until said liquor becomes more concentrated with respect topotassium compounds, adding to the mother liquor at some stage duringthe cycle of 5. A cyclic process of mining potassium com pounds fromunderground deposits thereof which comprises establishing a zonecontaining a main body of an aqueous mother liquor which is a solventfor said potassium compounds when unsaturated with respect thereto,withdrawing from said main body of mother liquor a portion thereof,heating said withdrawn portion of mother liquor whereby to produce asolvent liquor unsaturated with respect to the potassium compounds to bemined, passing said heated solvent liquor into a subterranean deposit ofsaid potassium compounds, circulating said solvent liquor in consiumchloride, the steps of cooling said concentrated liquor in one stage byreflux vaporization from self-contained heat of the liquor, andcoolingthe liquor in a second stage by vaporization of an added waterimmiscible volatile agent at least partially by the self-contained heatof the liquor, while separating solid potassium chloride therefromduring said cooling stages.

7. in a cyclic process of the character described for recovering apotassium compound from an ore containing it, the steps which compriseestablishing a zone containing a main body of a saline mother liquor,which is a solvent for said potassium compound when unsaturated withrespect thereto, continuously withdrawin from said main body of motherliquor a portion thereof, treating said withdrawn portion to increaseits dissolving action on said potassium compound, passing the treatedportion into contact with said ore containing said potassium compound tothereby increase the concentration of tact with said subterraneandeposit until said liquor becomes more concentrated with respect topotassium compounds, adding butane directly to the zone containing themain body of mother liquor, passing said more concentrated liquor intosaid main body of mother liquor to continuously volatilize said butane,condensing and returning to said zone the butane thus volatilized, saidmain body of mother liquor thereby being maintained at a relativelylower temperature than said more concentrated liquor, adding to saidmain body of mother liquor a suflicient amount of water to maintain theconcentration of dissolved solids with respect to the volume of solventliquor in said main body substantially constant, at least a-- portion ofsaid added water being derived by refiuxing the vapors arising from saidmain body, whereby the potassium compounds are precipitated withoutsubstantial precipitation or other compounds, and separating saidprecipitated potassium compounds from said main body of mother liquor. q

6. In a process of mining potassium chloride from an ore containing itwherein a heated solvent liquor rmsatm'ated with respect to potassiumchloride is circulated in contact with a subterranean deposit of the oreuntil said liquor becomes relatively more concentrated with respect topotasthe potassium compound therein, returning the more concentratedliquor to said main body of mother liquor, adding water to the main bodyof mother liquor to maintain the concentration substantially constantand to prevent the precipitation of other than potassium compounds, andseparating the potassium compound from said body of mother liquor.

8. In a process of mining potassium compounds from subterranean depositsthereof and'oi recovering potassium compounds therefrom wherein a heatedsolvent liquor unsaturated with respe'dt to the potassium compound iscirculated in contact with said subterranean deposit containing thepotassium compound until the liquor becomes more concentrated withrespect to the potassium compound, the steps of passing said moreconcentrated liquor into a substantially constant volume body of arelatively cooler mother liquor whereby the potassium compound isprecipitated, refluxing and returning to the body of said mother liquorthe vapors arising therefrom, separating the precipitated potassiumcompound from the both of said cooler mother liquor, ccm-' tinuouslyremoving aportion of said cooler mother liquor and continuously passingit'into heat archange relationship with said more concentrated hotliquor thereby to assist in cooling said more concentrated liquor and atthe same time causing said cooler mother liquor portion to be heated,

reheating said mother liquor portion further and recycling it as amining fluid in the process.

soreness.

